1. Field of the Invention
The present invention relates to an external electrode fluorescent lamp EEFL for a backlight, and more particularly, to an external electrode fluorescent lamp and a method for manufacturing the same, in which indentations are provided in a surface of a glass tube by etching when forming external electrodes at both ends of a fluorescent lamp.
2. Discussion of the Related Art
A Cathode Ray Tube (CRT) has been widely used as monitors in televisions, measuring machines, and information terminals. However, the CRT has limitations in size and weight. Accordingly, display devices such as liquid crystal display (LCD) devices using an electro-optics effect, plasma display panels (PDP) using gas discharge, and an electro luminescence display (ELD) devices using an electro-luminescence effect have been developed to replace the CRT.
LCD devices have been studied because LCD devices have great picture quality, low power consumption, and low heat dissipation as compared to CRTs. However, an LCD device does not emit light by itself, so that it is necessary to provide an additional light source. One solution is a reflecting-type LCD device using ambient light as a light source, but this has limitations in practical use due to the environment. In response, a transmitting-type LCD device having an additional light source has been developed, in which the additional light source is referred to as a backlight. An LCD device may use one of various light sources such as electro luminescence (EL), a light emitting diode (LED), a cold cathode fluorescent lamp (CCFL), or a hot cathode fluorescent lamp (HCFL). The CCFL having a long lifetime, low power consumption, and a thin profile is generally used for the light source.
In transmitting-type LCD devices, the backlight may be classified into a direct-type method and an edge-type method depending on the position of a fluorescent lamp. In the edge-type backlight, a tube-type fluorescent lamp is positioned at a side of the LCD panel, for transmitting the light from the fluorescent lamp to the entire surface of the LCD panel with a transparent light-guiding plate. Meanwhile, the direct-type backlight has been more widely used with large-sized LCD devices of 20-inch or more, in which a plurality of fluorescent lamps are placed below a lower surface of a light-diffusion plate, whereby the entire surface of the LCD panel is directly illuminated by the fluorescent lamps. At this time, the direct-type method, which has greater luminous efficiency as compared with that of the edge-type method, is used for large-sized LCD devices requiring high luminance. For example, the LCD device of the direct-type method is generally used for large-sized monitors or the televisions.
Hereinafter, a backlight for an LCD device according to the related art will be described with reference to the accompanying drawings.
FIG. 1 is a perspective view schematically illustrating a direct-type backlight according to the related art, and FIG. 2 illustrates a fluorescent lamp according to the related art.
As shown in FIG. 1, the direct-type backlight according to the related art includes a plurality of fluorescent lamps 1, an outer case 3, and light diffuser 5. In this example, the plurality of fluorescent lamps 1 are positioned along one direction at fixed intervals, and the outer case 3 maintains and supports the plurality of fluorescent lamps 1 at fixed intervals. Then, the light diffuser 5 is positioned above the plurality of fluorescent lamps 1. The light diffuser 5 prevents the silhouette of the fluorescent lamps 1 from being displayed on the display surface of the LCD panel (not shown), and for providing a light source having uniform luminance. For improving efficiency in diffusing light, a plurality of diffusion sheets and diffusion plates 5a, 5b, 5c may be provided. Also, a reflecting plate 7 is provided on an inner surface of the outer case 3 to concentrate the light emitted from the fluorescent lamps 1 to the display surface of the LCD panel, thereby improving the luminous efficiency. Also each fluorescent lamp 1 is fixed to holes provided at both sides of the outer case 3.
As shown in FIG. 2, the CCFL 1 is filled with a discharge gas, and electrodes 2 and 2a are provided, one electrode of a glass tube for applying power (not shown). Also, wires 9 are connected to the electrodes 2 and 2a. The wires 9 are also connected to an inverter (not shown) and a driving circuit. Each fluorescent lamp 1 requires an individual inverter.
However, the direct-type backlight according to the related art has the following disadvantages. In the direct-type backlight according to the related art, the silhouette of the CCFL may be displayed on the display surface of the LCD panel. Therefore, it is necessary to maintain a predetermined distance between the LCD panel and the CCFL. When using the direct-type backlight according to the related art, there are limitations as to how thin the LCD device may be. Also, hot cathode or cold cathode type electrodes are provided at the both ends of the glass tube in the related art fluorescent lamp. However, the process for providing the electrodes inside the fluorescent lamp is complicated, and each fluorescent lamp is driven with an individual inverter, thereby increasing manufacturing cost and the lifetime of the fluorescent lamp.